1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling packet error for in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
In LTE system, a media access control (MAC) layer provides data transfer services on logical channels. When MAC uses a physical downlink control channel (PDCCH) to indicate radio resource allocation, what kind of a radio network temporary identifier (RNTI) mapped on the PDCCH is used depending on the logical channel type, for example, a cell radio network temporary identifier (C-RNTI), a temporary C-RNTI and a Semi-Persistent scheduling C-RNTI are used for a dedicated control channel (DCCH) and dedicated traffic channel (DTCH), and a random access radio network temporary identifier (RA-RNTI) is used for random access response on a downlink share channel (DL-SCH). When a random access (RA) procedure is initiated by a PDCCH order or by the MAC sub layer, a MAC protocol data unit (MAC PDU) sent by the network is used to carry MAC random access response (MAC RAR) with timing information.
Please refer to FIG. 1, which is a schematic diagram of a MAC PDU in the prior art. As shown in FIG. 1, the MAC PDU consists of a MAC header and one or more MAC RARs and optionally padding. The MAC header is added at the beginning of a network packet in order to turn it into a frame ready for transmission over the network. The MAC header is of variable size and consists of one or more MAC sub-headers. Each MAC sub-header corresponds to a MAC RAR, except for a backoff indicator (BI) sub-header. Please refer to FIG. 2, which is a schematic diagram of the MAC sub-header of the MAC PDU shown in FIG. 1. As shown in FIG. 2, the MAC sub-header consists of three header fields E/T/RAPID. The BI sub-header consists of five header fields E/T/R/R/BI. The E field represents the extension field, which is a flag indicating if MAC sub-headers are present in the MAC header or not. The E field is set to “1” to indicate another set of at least E/T/RAPID or E/T/R/BI. The E field is set to “0” to indicate that a MAC RAR starts at the next byte. The T field, the type field, is a flag indicating whether the MAC sub-header contains a random access preamble identifier (RAPID) or a backoff indicator. The T field is set to “0” to indicate the presence of the backoff indicator field in the BI sub-header. The T field is set to “1” to indicate the presence of the RAPID field in the sub-header. The R field is a reserve bit, set to “0”. The BI field identifies the overload condition in the cell. The size of the BI field is four bits. The RAPID field identifies a random access preamble previously transmitted by the UE for initiation of the RA procedure. The size of the RAPID field is six bits.
Please refer to FIG. 3, which is a schematic diagram of a MAC RAR. The MAC RAR is of fixed size and consists of the following fields. The R field is a reserve bit, set to “0”. A timing advance (TA) command field indicates the index value TA (0-1282) used to control the amount of timing adjustment that the UE has to apply. The size of the timing advance command field is eleven bits. An uplink grant field indicates the resources to be used on the uplink. The size of the uplink grant field is twenty bits. A temporary C-RNTI field indicates the temporary identity that is used by the UE during random access procedure. The size of the Temporary C-RNTI field is sixteen bits.
As can be seen from the above, the MAC transmission associates with specific usage of RNTIs and packet formats. According to the LTE specification, when the MAC entity receives the MAC PDU identified by C-RNTI and Semi-Persistent scheduling CRNTI associated with the UE, namely, MAC PDU mapped to DTCH and DCCH, the MAC entity discards the received MAC PDU if the MAC PDU contains invalid values. However, for the MAC PDU mapped to a CCCH (Common Control Channel), there has been no error handling behavior specified yet.
In addition, during the RA procedure, when the MAC PDU related to MAC RAR is received, there has been no error handling behavior specified for the MAC RAR content so far. It is still unclear whether the UE shall consider the MAC RAR reception is unsuccessful if an invalid MAC RAR is received.